Various location determining systems (LDS) are used to determine the location of a mobile user. For example, a Global Positioning System (GPS) typically uses a set of twenty-four orbiting satellites to allow ground-based users to determine their locations. These systems provide the user with location information based on LDS such as GPS data. Some location systems include LDS elements integrated into a cellular phone, while others have equipment added to the wireless infrastructure.
Designing a location system has been cumbersome and involves manipulation and analysis of a variety of information. Location sensor density and geometry are extremely important to obtaining acceptable location data. For example, Angle of Arrival (AOA) techniques require sensor information from a minimum of two sites to obtain a location, three to estimate the quality of a location and a minimum of four to identify and reject severely corrupted (multipath) data from one site. Time Difference of Arrival (TDOA) techniques (both at the sites and in the handsets) require sensor information from a minimum of three, four, and five sites for the same capabilities. Factors such as the type of service area to be covered (rural vs. urban) or the characteristics of the wireless network (existing cell site densities, geometry of cell sites with respect to each other and areas to be covered, restrictions on antenna placement, availability at cell sites, etc.) are all factors affecting location performance and are incorporated in this software platform.
The geometry of the site infrastructure has a major impact on the quality of the locations. Geometric Dilution Of Precision (GDOP) plays an important role which must be considered. An extreme example of poor geometry is found along (relatively) straight highways between major cities. In these cases, cell sites are often located in a string near the highways providing cellular/PCS coverage only to the highway. An AOA location system with sensors located only at the sites will only be able to locate a mobile set as being between two highway sites. TDOA systems will only be able to locate the mobile set along a hyperbola intersecting the highway. This is at least better information if one can assume that the mobile set is on the highway and not on a nearby farm-to-market road. Even this would require a unique algorithm for use only in these areas. Note that a combined AOA/TDOA system would be able to provide location services under these circumstances.
Location systems have coverage requirements that conflict with those of Cellular/PCS networks. For example, an objective of a cellular/PCS design is to limit the radio coverage of a given base station. A location system, on the other hand, requires that each receiver site “see” (i.e., receive a useful signal) well beyond the limits of a single base station. A location system or technique generally operates the best, i.e., it offers the best accuracy for the highest percentage of the time, when it has an abundance of sites that receive the signal from the phone. This means that the higher the number of receiver sites that “see” the mobile unit the better the performance.
As explained above, because of the divergent requirements of wireless communication and wireless location systems, a specialized design and analysis software tool is required for proper design of a location system. There are a number of Cellular/PCS coverage design tools available on the market but none provide the utility to predict a location system coverage.
Therefore, there is a need for a software tool for analyzing wireless location systems with a user friendly graphical user interface (GUI).